The cross-connection problem per se is already known. Cross-connections are established by means of independent jumpers that provide the desired interconnections between connection boxes referred to as "optical cassettes". Thus, for example, the conductors of a "transport" cable are selectively connected to the conductors of one or more smaller capacity "distribution" cables via a first set of optical cassettes attributed to the transport cables, a second set of optical cassettes attributed to the distribution cables, and jumpers extending between the cassettes in the two sets. These two sets of cassettes and the interconnecting jumpers constitute a distribution frame or a subdistribution frame in a telephone or a computer transmission installation.
Each of the cables is fixed at one of its ends to its set of cassettes. Its rods, or pairs of conductors, or individual conductors are separated from one another at the cable fixing point, and they are guided to corresponding cassettes, and a certain amount of excess length of each of them is left in place. The cassettes serve to store the excess lengths, with the excess lengths being used for connection to jumpers, for establishing or changing connections.
Patent document FR-2 573 544 in particular describes a cassette of this type. That cassette has a bottom on which the following are defined on a single side thereof: an outer ring between an outer wall and an inner wall; and an inner ring between the above-mentioned inner wall and at least one central cylinder. The rings are used for storing excess cable conductor length(s) together with conductor(s) of a jumper cable, with the conductors being interconnected inside the cassette by one or more connector devices in the form of an optical connector strip. Tabs on the edges of these walls and of the cylinder serve to hold the excess lengths inside the cassette.
With a cassette of this type, any action on the connector device leads to excess conductor lengths from both cables being manipulated in order to separate the conductors and change the connections.
In the Applicants' patent application FR 89 16813 proposals are made for a different type of cassette referred to as a "two-compartment" cassette having a plate at one of its ends extending the cassette and designed to receive a block of optical connectors. The compartments of that cassette are used for storing respectively a first excess length and a second excess length of a single optical conductor or of several optical conductors. Each conductor is held where it passes from one compartment to another to enable one of its excess lengths to be manipulated without affecting the other excess length thus made independent therefrom which remains coiled down in its own compartment.
Thus, one of the excess lengths is used for extracting one of the cassettes from a stack of cassettes, while the other one is used for changing or correcting a connection under conditions of use.
An object of the present invention is to simplify conditions of use as much as possible and to make it particularly easy and quick to make optional connection changes and to establish interconnections within distribution frames.